Flexible Reservation Research Articles

A Frequency Security Constrained Scheduling Approach Considering Wind Farm Providing Frequency Support and Reserve

The proposal of the “carbon neutrality” target promotes the rapid development of variable renewable energy, which leads to the reduction of inertia and the deficiency of flexible reserve in power systems. Wind turbines (WTs) now are asked for providing frequency support and reserve through proper control strategy. This proposes a new issue on how to coordinate the operation of conventional units and WTs. This paper proposes a frequency security constrained scheduling approach considering wind farms providing frequency support and reserve. Two dynamic frequency indices: RoCoF and nadir, are derived and introduced into the scheduling model. The frequency support capability of wind farm is accurately quantified by considering the real grid-connected WT capacity and wake effect. A wind power reserve model considering uncertainty is established by linking the reserve under the forecasted scenario and uncertain scenarios through reserve auxiliary variables. The contribution of wind farms to power system frequency support and reserve is quantified in the robust scheduling model. Case studies show that the frequency support and reserve from wind farms can effectively reduce the whole operation cost and VRE curtailment. Moreover, the value of wind farms in CO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> emission reduction is properly quantified.

Building Load Control Using Distributionally Robust Chance-Constrained Programs with Right-Hand Side Uncertainty and the Risk-Adjustable Variants

Aggregation of heating, ventilation, and air conditioning (HVAC) loads can provide reserves to absorb volatile renewable energy, especially solar photo-voltaic (PV) generation. In this paper, we decide HVAC control schedules under uncertain PV generation, using a distributionally robust chance-constrained (DRCC) building load control model under two typical ambiguity sets: the moment-based and Wasserstein ambiguity sets. We derive mixed integer linear programming (MILP) reformulations for DRCC problems under both sets. Especially, for the Wasserstein ambiguity set, we use the right-hand side (RHS) uncertainty to derive a more compact MILP reformulation than the commonly known MILP reformulations with big-M constants. All the results also apply to general individual chance constraints with RHS uncertainty. Furthermore, we propose an adjustable chance-constrained variant to achieve tradeoff between the operational risk and costs. We derive MILP reformulations under the Wasserstein ambiguity set and second-order conic programming (SOCP) reformulations under the moment-based set. Using real-world data, we conduct computational studies to demonstrate the efficiency of the solution approaches and the effectiveness of the solutions. Summary of Contribution: The problem studied in this paper is motivated by a building load control problem that uses the aggregation of heating, ventilation, and air conditioning (HVAC) loads as flexible reserves to absorb uncertain solar photovoltaic (PV) generation. The problem is formulated as distributionally robust chance-constrained (DRCC) programs with right-hand side (RHS) uncertainty. In addition, we propose a risk-adjustable variant of the DRCC programs, where the risk level, instead of being predetermined, is treated as a decision variable. The paper aims to provide tractable reformulations and solution algorithms for both the (general) DRCC and the (general) adjustable DRCC models with RHS uncertainty.

A Study on the Impact of Financial Flexibility on Corporate Value: Moderating Effects Based on Environmental Uncertainty and Agency Costs

Purpose The purpose of this article is to understand the financial flexibility reserves of listed companies in China. Based on the internal and external environment of China’s listed manufacturing companies, it studies the impact of financial flexibility on corporate value. Design/Methodology/Approach Based on the trade-off theory, this paper studies the impact of financial flexibility on corporate value. According to the resource-based theory, environmental uncertainty and agency cost are selected from the internal and external factors of the enterprise, and financial contingency theory and principal-agent theory are introduced to analyze their influence mechanism on the relationship between financial flexibility and enterprise value. According to the research results, corresponding suggestions are made to the government and enterprises respectively. Findings This paper studies the impact of financial flexibility on corporate value. Financial flexibility can significantly increase the corporate value of listed companies. Environmental uncertainty plays a positive role in regulating the positive impact of financial flexibility on corporate value. The moderating effect of agency costs between financial flexibility and corporate value has not been proven. Research Implications In the management of this paper, this article provides strong empirical support for the establishment of an effective financial flexibility reserve mechanism and the improvement of corporate value. At the same time, it provides an important theoretical basis for the government’s policy of “structural deleveraging to resolve financial risks” during the transition period, and also provides a reference for the steady advancement of Chinese enterprises’ deleveraging work.

Stochastic Optimal Scheduling ConsideringMultiple Flexible Reserve Resources on Both Source and Load Sides

Stochastic Optimal Scheduling ConsideringMultiple Flexible Reserve Resources on Both Source and Load Sides

Wind power ramp event detection using a multi-parameter segmentation algorithm

The variable nature of wind power and the associated ramp events poses a number of operational challenges to grid operators, especially under high penetration of wind energy. These challenges typically relate to system stability, frequency control and dispatch. The adverse impacts of wind power ramps can be mitigated in practice through optimal scheduling and dispatch of flexible reserves and rapid response ancillary services. This, however, requires appropriate ramp detection algorithms, together with accurate ramp forecasting. This paper proposes a novel multi-parameter segmentation algorithm for the detection of wind power ramps. Ramp detection results are presented for a utility-scale wind farm, and the performance of the proposed algorithm is compared with existing algorithms, including the L1-ramp detect with sliding window and the optimized swinging door algorithm. The results show that the proposed algorithm is superior, particularly with reference to criteria such as ramp detection accuracy, computational expedience and ramp start- and end-point accuracy.

Energy flexibility curves to characterize the residential space cooling sector: The role of cooling technology and emission system

Space cooling of buildings shows an increasing trend in energy use worldwide. The exploitation of the energy flexibility reserve obtainable from buildings cooling-loads management can have an important role to improve the security and the reliability of the electricity power grid. Many studies in literature assess the energy flexibility potential of air conditioning systems; however, the role of the specific cooling technology is always scarcely explored. The objective of this work is to provide an evaluation of the operational energy flexibility that can be obtained involving the most common residential space cooling technologies, paying particular attention to the distribution system (e.g., all-air system, fan-coil units with and without the addition of a thermal energy storage and hydronic massive systems). The analysis is carried out with dynamic simulation models for the various cooling systems involved. Results show a great influence of the adopted distribution system in the implementation of a flexibility request. In particular, all-air systems (i.e. split systems) show the lower flexible behavior (they require up to 10 h of precooling to be off during a peak hour). Whereas the adoption of fan coil units coupled with a thermal energy storage allows to implement different peak shaving strategies without compromising the indoor air temperature with low drawback effects in terms of anticipated electricity overconsumptions (no precooling of the air is required and a maximum of 23 % increase in electricity consumed in the time before the event occurs, with a reduction of 16 % in subsequent hours). In case of ceiling cooling systems, results highlight that as the thermal inertia of the system increases, the indoor conditions are less affected, but the anticipated overconsumption of the heat pump increases (for the same Demand Response event the electricity overconsumption goes from + 67 % to +116 %, passing from ceiling panels to concrete ceiling). The results obtained from this analysis are then used to draw flexibility curves, which aim at providing a characterization of the flexibility of a cooling system. They can be used to predict, for typical installations, the system behavior in presence of a peak power reduction strategy in terms of pre-cooling duration, energy use variation and modification of the temperature comfort bandwidth. Such predictions are important because they can provide insights on the design and operation of space cooling systems in demand side management strategies.

Flexibility Reserve of Self-Consumption Optimized Energy Systems in the Household Sector

Energy generation and consumption in the power grid must be balanced at every single moment. Within the synchronous area of continental Europe, flexible generators and loads can provide Frequency Containment Reserve and Frequency Restoration Reserve marketed through the balancing markets. The Transmission System Operators use these flexibilities to maintain or restore the grid frequency when there are deviations. This paper shows the future flexibility potential of Germany’s household sector, in particular for single-family and twin homes in 2025 and 2030 with the assumption that households primarily optimize their self-consumption. The primary focus is directed to the flexibility potential of Electric Vehicles, Heat Pumps, Photovoltaics and Battery Storage Systems. A total of 10 different household system configurations were considered and combined in a weighted average based on the scenario framework of the German Grid Development Plan. The household generation, consumption and storage units were simulated in a mixed-integer linear programming model to create the time series for the self-consumption optimized households. This solved the unit commitment problem for each of the decentralized households in their individual configurations. Finally, the individual household flexibilities were evaluated and then aggregated to a Germany-wide flexibility profile for single-family and twin homes. The results indicate that the household sector can contribute significantly to system stabilization with an average potential of 30 GW negative and 3 GW positive flexibility in 2025. In 2030, the corresponding flexibilities potentially increase to 90 GW and 30 GW, respectively. This underlines that considerable flexibility reserves could be provided by single-family and twin homes in the future.

Dynamic tests of the collapse-prevention performance of a low-ductility low-rise steel concentrically braced frame

In past earthquakes, low-ductility steel concentrically braced frame (CBF) buildings have been observed to retain reserve capacity after brace fracture. The failure mechanisms and earthquake ground motion-sensitive characteristics of the reserve system of low-ductility CBFs are not understood due to limited dynamic experimental data. In this study, a series of shaking table tests is presented to examine the reserve capacity of a scaled two-bay, three-story, low-ductility CBF model in which a pair of square hollow section braces are arranged in a chevron pattern. The model structure was repeatedly subjected to two unidirectional ground motions with successively increasing magnitudes in a stiff soil site and a soft soil site. The experimental phenomena of elastic response, brace buckling behavior, brace reengagement behavior, reserve system response and collapse state were observed. The braces of the low-ductility CBFs were vulnerable to local buckling under dynamic loads and resulted in a soft story where braces failed, while braces and frames in the other stories had no further damage. The reserve stiffness, rather than energy dissipation or reserve strength, was the most important factor in the collapse-prevention capacity for the reserve system of the tested low-ductility CBF, and the lateral stiffness of the columns was the main source of reserve stiffness. Flexible reserve systems with small lateral stiffness were never significantly excited at their natural periods by hard soil site-specific ground motions, while with such systems, a greater risk of potential collapse appears to be posed due to earthquakes at soft soil sites than at hard soil sites for the test model.

Transactive Energy-Based Joint Optimization of Energy and Flexible Reserve for Integrated Electric-Heat Systems

Implementing integrated electric-heat systems (IEHSs) with coupled power distribution networks and district heating networks is an essential means to solve current energy problems. However, prosumers with multiple energy forms coupled and renewable energy sources with natural uncertainties pose challenges to the operation of IEHSs. This paper proposes a joint energy and reserve dispatch model for IEHSs based on transactive energy, which is a coordinated combination of a bi-level Stackelberg game and two-stage robust optimization. The bi-level Stackelberg game is used to realize the equilibrium of interests among three transacting parties, namely, integrated energy service provider (IESP), multi-carrier prosumer (MCP), and load aggregator (LA). The two-stage robust optimization is employed to ensure the reliability of the system operation under renewable energy uncertainty. In the upper level of the Stackelberg game, the IESP perform pricing and reserve dispatch, while the MCP and LA maximize their benefits via energy management in the lower level. Linearization techniques are utilized to approximate the bi-level Stackelberg game model into a single-level mixed-integer linear programming problem. The converted single-level game model is subsequently regarded as the first stage, while the real-time feasibility check is regarded as the second stage to form a two-stage robust optimization model, which is solved by a modified C&CG algorithm. Case studies demonstrate that the proposed joint energy and reserve dispatch method effectively achieves economic and reliable operation.

Flexible Operation of Hybrid Distributed Energy System Based on Reliability Redundancy

This paper establishes a reliable-economic power sharing scheme of distributed energy system (DES) consists of Li-ion storage battery and photovoltaic (PV) source connected to the utility grid through a distribution feeder. The system is intended to supply a vehicle charging station that requires dense energy production for efficient and short time charging process. Therefore, the issue of battery state-of-charge (SOC) optimal scheduling and power routing among the sources are considered as a technical-economic problem from system dynamic reliability point of view. In the developed optimization framework, the required energy reserve, the optimal SOC scheduling, and the impact of the station on the utility grid are considered and investigated. A new PSO based optimization is proposed to optimize the power sharing of the sources using reliability based optimal power flow scheduling. The proposed methodology quantifies the reliability redundancy of the system to reliably dispatch the power between the sources. The reliability redundancy concept is proposed as a tool to dynamically schedule the battery SOC and updates the power dispatching among the sources in order to: (1) establish a flexible reserve margin, (2) increase the overall number of battery charging/ discharging cycles, (3) economically dispatch the power, and (4) provide an indirect grid service by decreasing the impact of the charging station on the utility grid. The results show that the system reliability is maintained and the number of accumulated cycles is increased by 134 cycles. Furthermore, the maximum imported grid power is decrease from 40.0 kW to 28.3 kW.

Ancillary services in the Indian power sector – A look at recent developments and prospects

Reliable and secure operation of a power system depends on the ability of system operation to address system imbalances on account of demand-supply imbalances and that an account of change in availability of transmission network elements. The impact of a power plant or transmission line failures causes a short-term imbalance between generation and demand, and balance can be addressed by deploying flexible reserves and ancillary services. The system imbalances in the Indian power system operation are addressed through Deviation Settlement Mechanism, a commercial mechanism based on a frequency linked incentive/penalty structure. Implementation of reserve regulation ancillary services in India has further helped to address deviation in frequency, congestion, and to bring grid resilience. This paper discusses the development of ancillary services in India, alongside crucial developments in the power market. Given the ongoing developments in the Indian power market and international experiences, this paper suggests a road map for further development of the ancillary services market in the country. The Indian power system has also witnessed a significant growth of variable renewable energy resources. In the future, renewable resources are expected to provide full range ancillary services ensuring the least cost, supply security, and high availability of reserves. Deviations on account of uncertainty associated with renewable resource generation are also subject to Deviation Settlement Mechanism, although with lenient penalties.

Flexibility and Operating Reserves in Electric Power Systems

Maintaining the efficiency of electric power systems (EPSs) requires some flexibility margin, which decreases in the case of adopting a variety of renewable energy sources (RESs). For this reason, the determination of the EPS flexibility several hours ahead becomes especially urgent. In this study, the flexibility of a 5-node EPS with a four-minute load change during a 6-hour time horizon is calculated. To this end, a probabilistic method based on the analysis of the cumulative probability of the available flexibility is used.

Analysis of the Influence of Financial Flexibility on Enterprises

Through the analysis of empirical papers on financial flexibility over the years it can find that the impact of financial flexibility on corporate value shows a trend of increasing first and then decreasing, and there is an inflection point. Financial flexibility reserve is helpful to reduce the credit risk of the enterprise and help the enterprise to buffer under the environment of greater uncertainty. This buffer is more obvious when the financing constraint is greater. At the same time, this paper puts forward relevant suggestions on how to improve the financial flexibility of enterprises: increase the proportion of equity funds, increase capital reserves, and choose appropriate dividend policies.

Flexible Robust Risk-Constrained Unit Commitment of Power System Incorporating Large Scale Wind Generation and Energy Storage

With the increasing penetration of wind power in the power systems, the uncertainties in wind power significantly challenge the reliable and economic operation of power systems. Recently, the worst scenario-based robust optimization approaches have been employed to manage the uncertainties in the unit commitment problem. To further improve the robustness and economic efficiency of power system operation, this article proposes a flexible robust risk-constrained unit commitment formulation, in which flexible reserve capacities of conventional generators and energy storage are allocated to cope with the uncertainty of wind power. The proposed model optimizes the unit commitment and dispatch solutions for the base case while guaranteeing that the flexible reserve capacity can be adaptively adjusted after wind generation realization. In contrast to the predefined uncertainty set in the conventional robust unit commitment, the proposed model constructs an adjustable and flexible uncertainty set via balancing the operational costs and the operational risk. The model establishes worst-case constraints to optimally allocate the flexible reserve capacity. The proposed model can be equivalently transformed into a single-level optimization problem using the strong duality theory. Numerical case studies on a modified standard test system demonstrate the effectiveness and the efficiency of the proposed model.

Flexible parking reservation system and pricing: A continuum approximation approach

Reservation-based parking systems have the merit of eliminating vehicle cruising for parking. While many long-period (e.g., daily) parking reservation services are already in use, short-period (e.g., hourly) parking reservation remains a huge challenge due to the high uncertainty of customer arrivals and departures. To mitigate the service failure caused by random late departures of customers, we propose a new flexible reservation mechanism in which the reservation is no longer restricted to a specific location at a specific time, but tolerates predetermined spatiotemporal flexibility instead. With a pricing instrument designed for such parking flexibility, customers can coordinate to significantly reduce the reservation failure rate, resulting in an optimal system equilibrium benefiting the entire society. Due to the complex nature of this system, a continuum approximation framework is used to provide tractable analysis for a large-scale urban parking system. We can successfully provide accurate system management decision support with a bounded optimality gap and analytical insights.

Flexibility Reserve in Power Systems: Definition and Stochastic Multi-Fidelity Optimization

This paper defines flexibility reserve trajectory as a single reserve product that not only supplies the energy imbalance in real-time operation but also the resulting ramping requirements by embedding the flexible ramping trajectories as time derivative of the reserve trajectories. Further, a stochastic optimization model is proposed for multi-fidelity co-optimization of energy and flexibility reserve in day-ahead power systems operation. The proposed model integrates operation decisions with different levels of modeling fidelity in a single stochastic optimization problem. More specifically, day-ahead energy trajectories, day-ahead flexibility reserve capacity trajectories, and real-time flexibility reserve deployment trajectories are modeled by Bernstein polynomials with different degrees as required to match the load and renewable generation with different levels of variability in day-ahead and real-time operations. The proposed model is implemented on the IEEE reliability test system using load and solar generation data of California ISO, where the numerical results demonstrate that the proposed model schedules a reserve capacity that more accurately matches the real-time energy imbalance and ramping requirements of net-load, while reducing the total operation cost of the system.

Stochastic Multi-Fidelity Scheduling of Flexibility Reserve for Energy Storage

This paper proposes a continuous-time two-stage stochastic optimization model for multi-fidelity co-optimization of energy and flexibility reserve provided by generating units and energy storage (ES) devices in day-ahead operation. The flexibility reserve, defined as a single continuous-time trajectory that combines the balancing and ramping reserves, not only supplies the energy deviation but also the ramping requirements of load and renewable generation in power systems operation. The proposed model co-optimizes decision variables with different modeling fidelity, where the energy and flexibility reserve schedules are modeled and optimized by Bernstein polynomials of different degrees to match the flexibility requirements of load and renewable generation in day-ahead and real-time operation stages. Numerical studies, conducted on the IEEE reliability test system with the load and solar data of California ISO, highlight the benefits of the proposed stochastic multi-fidelity model over traditional discrete-time models in efficient utilization of ES flexibility to supply the energy and ramping requirements of the net-load and avoid scarcity events.

Operating Reliability Evaluation of Power Systems Considering Flexible Reserve Provider in Demand Side

The development of information and communication technologies and the deregulation of power systems have made the flexible demand participation in bidirectional interaction with power grid possible. The flexible demand can be represented as the flexible reserve provider (FRP) to provide operating reserve through load curtailment and shifting for assisting power system operation. However, the chronological characteristics of curtailment and shifting of FRP may impact the reliability of power systems. Moreover, the uncertainties from customers’ participation performances, random failures of information and communication system, and different load types may also influence system operation. In this paper, a novel operating reliability evaluation model for power systems with FRP is proposed utilizing reliability network equivalent (RNE) and time-sequential simulation (TSS) techniques. The RNE technique is developed to include the reserve capacities of FRP incorporating both chronological characteristics and uncertainties. Optimal operation dispatch for system contingencies considering co-optimization of generation and FRP deployment amount is formulated over the entire study period. The TSS method is utilized to assess the operating reliability of restructured power systems. The proposed approaches are validated using the modified IEEE RTS.

Flexibility Based Day-Ahead Generation–Reserve Bilevel Decision Model

With the increasing penetration rate of renewable energy like fluctuating wind and solar energy, the power system has to equip itself with a more reasonable reserve capacity. Therefore, how to quantify the reserve capacity needed for dealing with the uncertainty and fluctuation has turned out to be a new problem faced by the power system integrated with large-scale renewable energy. This paper proposes a flexibility based day-ahead generation–reserve bilevel decision model. In the upper level, the day-ahead unit commitment model is constrained by flexibility reserve, which is calculated in the lower level. In the lower level, taking into account various factors of uncertainty and fluctuation, e.g., wind power ramping, load ramping and random failure of conventional units, the ramping probability distribution of an equivalent system is obtained by the universal generating function method, then the quantified relationship between operating reserve and flexibility is established ultimately. If the unit commitment scheme gained from the upper level could not provide sufficient reserve, a feedback for the correction of the upper level is needed. The rationality and validity of the proposed model are verified through the simulation of a modified IEEE-118 bus system.

Environmental Dynamics, Financial Flexibility and Enterprise Strategic Change

Enterprise strategic change is affected by the external environment, so the research on the relationship between external environment and strategic change has always been concerned by academic circles. Based on contingency theory and resource-based theory, this paper analyzes the influence of environmental dynamics on the strategic change of manufacturing enterprises, and explores how corporate financial flexibility adjusts the relationship between environmental dynamics and strategic change. Taking the 2011-2017 A-share listed manufacturing companies in Shanghai and Shenzhen stock markets as the research object, the empirical results show that: 1) the environmental dynamism is positively related to strategic change—the more dynamic the environment is, the more the manufacturing enterprise inclined to implement the strategic change; 2) financial flexibility positively regulates the impact of environmental dynamics on strategic change. The high level of financial flexibility means abundant resources for strategic change, and the greater the role of environmental dynamism in promoting the implementation of strategic change by manufacturing enterprises. This paper deepens the research on the impact of environmental dynamism on enterprise strategic change, and introduces financial flexibility as a moderating variable, which enriches the theoretical system of strategic change. At the same time, this paper takes manufacturing enterprises as the research object to provide theoretical and practical guidance for Chinese manufacturing enterprises to optimize financial flexible reserve according to the dynamic degree of the environment to successfully implement strategic change.